1. Field of Invention
The invention relates to a seat assembly with a seat base, with a back support and with a support for the back support and/or the seat base, wherein the back support and/or the seat base are/is pivotably arranged on the support in such a manner that a pivoting movement of the back support and/or of the seat base on a rotation axis can be carried out, and wherein the seat assembly comprises at least one elastomer torsion-spring element for transmitting a force between the back support and the support and/or for transmitting a force between the seat base and the support.
2. Related Art
For example, elastomer torsion-spring elements are known which comprise an internal casing, an external casing that encompasses the internal casing and an elastomer body arranged in a space between the internal casing and the external casing. In this arrangement the internal casing as a rule comprises at least one contact surface at which the elastomer body is in contact with the internal casing, while the external casing comprises at least one contact surface at which the elastomer body is in contact with the external casing. Furthermore, the internal casing and/or the external casing of the respective elastomer torsion-spring element are/is rotationally arranged on a rotation axis, and rotation of the internal casing and/or of the external casing by a rotation angle on the rotation axis can be carried out in such a manner that during the respective rotation the internal casing is moved relative to the external casing, and in this process deformation of the elastomer body is generated so that the elastomer body generates a restoring torque between the external casing and the internal casing, which restoring torque acts against the rotation.
Such an elastomer torsion-spring element is, for example, used in devices for transmitting power between bodies that can be moved relative to each other in order to, during movement of a first body relative to a second body, generate a restoring force that counteracts the respective movement. If a first force acts on the first body and consequently moves the first body relative to the second body, the respective device for transmitting power causes, for example, the device for transmitting power to generate a restoring force that counteracts the first force so that the first body can assume an equilibrium position relative to the second body, wherein in the equilibrium position the first force is compensated for by the respective restoring force.
Such a device for transmitting power between a first body and a second body which is movable relative to the first body can be implemented with the use of at least one elastomer torsion-spring element of the type mentioned above, and with the use of a first coupling means for coupling the first body to the external casing of the respective elastomer torsion-spring element and a second coupling means for coupling the second body to the internal casing of the respective elastomer torsion-spring element. For this purpose the first coupling means and the second coupling means can, for example, be designed in such a manner that the first body can be coupled to the external casing of the respective elastomer torsion-spring element in such a manner and the second body can be coupled to the internal casing of the respective elastomer torsion-spring element in such a manner that during movement of the first body relative to the second body rotation of the internal casing and/or of the external casing by a rotation angle on the rotation axis is carried out, in which rotation the internal casing is moved relative to the external casing and in this process deformation of the elastomer body is generated. In this arrangement the elastomer body of the respective elastomer torsion-spring element generates a restoring torque between the respective external casing and the respective internal casing, which restoring torque acts against the rotation of the internal casing or of the external casing. In this arrangement the restoring torque generated by the respective elastomer torsion-spring element corresponds to a restoring force that counteracts the respective movement of the first body relative to the second body.
Devices for the transmission of power according to the type mentioned above are used in many technical applications in the field of machine construction.
One field of application of such devices for transmitting power relates, among other things, to seat assemblies, for example chairs.
Seat assemblies are frequently designed so as not to be rigid; instead they usually comprise a support structure arranged in a fixed manner, and a back piece that can be pivoted relative to the support structure and/or a seat base that can be pivoted relative to the support structure, in order to make it possible, for example, on the one hand to adapt the spatial arrangement of the back piece and/or of the seat base to the respective body posture of a person seated on the respective seat assembly, which person continually varies their body posture, or, for example, to make it possible for the same seat assembly to be adapted to different requirements of different persons, for example of different body size or different body weight or different habits relating to their preferred body posture. In this case a device for transmitting power of the type mentioned above can advantageously be used to couple the back piece by way of the respective elastomer torsion-spring element to the support structure, and thus to make it possible, if a force acts on the back piece, for said back piece to be pivoted relative to a predetermined normal position and the respective elastomer torsion-spring element during the respective pivoting movement of the back piece to generate a restoring force that acts on the back piece or generates a restoring torque that acts on the back piece in order to in each case hold the back piece in a stable equilibrium position. The latter improves seating comfort. Correspondingly, a device for transmitting power of the type mentioned above can be used to couple a seat base of the seat assembly by way of the respective elastomer torsion-spring element to the support structure.
EP 1486142 A1 shows a chair comprising an elastomer-elastomer torsion-spring element 258 of the type mentioned above, which element is used to generate a restoring torque that counteracts a pivoting movement of a seat support on a rotation axis. The elastomer torsion-spring element 258 comprises an internal casing 260 and an external casing 264, wherein in a space between the internal casing 260 and the external casing 264 an elastomer body 262 has been incorporated. The internal casing 260 on its exterior comprises a contact surface at which the elastomer body 262 is in contact with the internal casing 260, and the external casing 264 on its interior comprises a contact surface at which the elastomer body 262 is in contact with the external casing 264. In this arrangement the elastomer body 262 is rigidly connected to the respective contact surface of the internal casing 260 and to the respective contact surface of the external casing 264 so that the elastomer body 262 cannot slip relative to the internal casing or to the external casing either on the contact surface of the internal casing 260 or on the contact surface of the external casing 264.
The external casing 264 and the internal casing 260 are designed so as to be cylindrical and are arranged coaxially relative to each other. The external casing 264 is held to a support structure of the chair, while the internal casing 260 is seated in a rotationally fixed manner on a shaft 250 that is rotatable on its longitudinal axis. A seat base 32 of the chair is coupled to the shaft 250 in such a manner that if the weight of a person acts on the seat base 32 the shaft 250 is rotated on its longitudinal axis and the seat base 32 is pivoted from a predefined normal position. As a result of rotation of the shaft 250 the internal casing 260 is rotated on its longitudinal direction and in this process is rotated relative to the external casing 264, and consequently the elastomer torsion-spring element 258 generates a restoring torque that acts on the shaft 250 or on the seat base 32, which restoring torque counteracts the rotation movement of the shaft 250 or the pivoting movement of the seat base 32 and increases as the rotation angle increases. In the case of the elastomer torsion-spring element 258 the extent of the minimum torque acting on the shaft 250 when the seat base 32 is pivoted from the above-mentioned normal position (hereinafter referred to as the “minimum restoring torque”) can be changed, for example depending on the body weight of the person seated on the chair. For this purpose the external casing 264 can be rotated on its longitudinal axis by means of a rotary mechanism that is arranged on the support structure of the chair, and can thus be rotated on the longitudinal axis of the shaft 250, wherein the external casing 264 is rotated relative to the support structure of the chair and relative to the internal casing 260 or to the shaft 250. By means of rotating the external casing 264 relative to the internal casing 260 the elastomer torsion-spring element 258 is pre-tensioned, wherein the rotation angle by which the external casing 264 is rotated relative to the internal casing 260 when the seat base 32 is in the normal position determines the extent of the “minimum restoring torque”.
Due to the cylindrical shape of the external casing 264 and of the internal casing 260 the contact surfaces of the external casing 264 and of the internal casing 260, which contact surfaces in each case adjoin the elastomer body 262, are circular, in each case in a sectional plane that is perpendicular to the shaft 250. During rotation of the shaft 250 on its longitudinal direction the elastomer body 262 is deformed in such a manner that it is subjected to tensile loads.
The elastomer torsion-spring element 258 is associated with a disadvantage in that the restoring torque that is generated during rotation of the shaft 250 by a certain rotation angle shows a relatively slight rise as a function of the respective rotation angle, in particular in those cases where the elastomer torsion-spring element 258 is not pre-tensioned or is only slightly pre-tensioned. This leads to a further disadvantage in that the elastomer torsion-spring element 258 needs to be pre-tensioned to a very high extent if a large minimum restoring torque is to be set, for example in order to provide appropriate seating comfort to a person of substantial body weight. Furthermore, the restoring torque as a function of the rotation angle of the shaft 250 increases in a strongly nonlinear (progressive) manner if the shaft 250 is, for example, to be rotated by a rotation angle ranging from 0 to approx. 70°. In the context of applications relating to seat assemblies, substantial nonlinearity of the restoring torque in the above-mentioned rotary angle range is undesirable because such nonlinearities are, as a rule, perceived by users to be disagreeable. Thus the available rotary angle range is reduced, which is uncomfortable. In addition, as a result of the substantial pre-tension the elastomer body 262 is permanently exposed to considerable load, and consequently experiences fatigue earlier. Consequently, the elastomer torsion-spring element 258 has a short service life and needs to be frequently replaced. There is a further disadvantage in that setting the respective pre-tension of the elastomer torsion-spring element 258 is cumbersome and time consuming, all the more so since the external casing 264 needs to be adjusted by a large angle relative to the internal casing 260 for a minimum restoring torque to be set.
From GB 2070727 A a further elastomer torsion-spring element of the type mentioned above is known. This elastomer torsion-spring element is used in a device for transmitting power between a base plate and a motor that is held so as to be movable relative to the base plate. This elastomer torsion-spring element also comprises an internal casing and an external casing that encompasses the internal casing, wherein the internal casing and/or the external casing are/is rotatably arranged on a rotation axis. The external surface of the internal casing and the internal surface of the external casing comprise a cross section in the form of a square in a sectional plane that is perpendicular relative to the rotation axis. There is a space between the internal casing and the external casing. In the “normal position” the internal casing of the elastomer torsion-spring element is rotated by 45° on the rotation axis relative to the external casing so that in this case the space essentially comprises four subregions formed in the region of the four corners of the external casing and which have the shape of a triangle when viewed in a cross section perpendicular to the rotation axis. In each of these four subregions in each case an elastomer body (preferably comprising rubber) is inserted. In its non-deformed state the respective elastomer body has a cylindrical shape. Prior to placement in the respective subregions of the space, the elastomer bodies are in each case compressed and in the compressed state are inserted in the respective subregion of the space in such a manner that each of the subregions is essentially taken up by one of the elastomer bodies, and each of the elastomer bodies rests at a certain pressure against the external surface of the internal casing and against the internal surface of the external casing, wherein the elastomer body is not rigidly connected either to the internal casing or to the external casing. In each case the four elastomer bodies of this elastomer torsion-spring element are identical so that the internal casing of the elastomer torsion-spring element is held in the above-mentioned normal position by the elastomer bodies, provided no external forces act on the external casing or on the internal casing, which external forces could rotate the internal casing relative to the external casing on the rotation axis. However, if the internal casing is rotated on the rotation axis relative to the external casing, then the four elastomer bodies generate a restoring torque between the internal casing and the external casing, which restoring torque counteracts the respective rotation movement and increases as the rotation angle increases. This elastomer torsion-spring element is associated with various disadvantages. The internal casing can at most be rotated on the rotation axis by approx. 30° relative to the external casing, namely to the same extent in both directions of rotation. Rotating movements by more than 30° when compared to the normal position are not practicable. During rotation of the internal casing the restoring torque of this elastomer torsion-spring element increases by a rotation angle (relative to the above-mentioned normal position in relation to the external casing) as a function of the rotation angle in a range from 0 to 30° with substantial nonlinearity. Furthermore, when the internal casing is rotated by more than 30° relative to the internal casing or to the external casing there is a danger of the elastomer bodies slipping. In this arrangement the internal casing can move to an unstable position so that the elastomer bodies are no longer able to generate a restoring torque that can reliably move the internal casing back to the respective normal position relative to the external casing. In many applications such instability is undesirable and may need to be prevented, for example with the use of safety measures that block further rotation of the internal casing when rotating the internal casing relative to the normal position attains a critical limit of approx. 30° relative to the normal position.